Throughout this application, various publications are referenced by arabic numerals within parentheses. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of art as known to those skilled therein as of the date of the invention described and claimed herein.
Superoxide dismutase (SOD) and the phenomenon of oxygen free radicals (O.sub.2 --) was discovered in 1968 by McCord and Fridovich (1). Superoxide radicals and other highly reactive oxygen species are produced in every respiring cell as by-products of oxidative damage to a wide variety of macromolecules and cellular components (for review see 2,3). A group of metalloproteins known as superoxide dismutases catalyze the oxidation-reduction reaction 20.sub.2 --+.sub.2 H.sup.+ .fwdarw.H.sub.2 O.sub.2 +O.sub.2 and thus provide a defense mechanism against oxygen toxicity.
There are several known forms of SOD containing different metals and different proteins. Metals present in SOD include iron, manganese, copper and zinc. All of the known forms of SOD catalyze the same reaction. These enzymes are found in several evolutionary groups. Superoxide dismutases containing iron are found primarily in prokaryotic cells. Superoxide dismutases containing copper and zinc has been found in virtually all eukaryotic organisms (4). Superoxide dismutases containing manganese have been found in organisms ranging from microorganisms to man.
Since every biological macromolecule can serve as a target for the damaging action of the abundant superoxide radical, interest has evolved in the therapeutic potential of SOD. The scientific literature suggests that SOD may be useful in a wide range of clinical applications. These include prevention of oncogenesis and of tumor promotion, and reduction of the cytotoxic and cardiotoxic effects of anticancer drugs (10), protection of ischemic tissues (12) and protection of spermatozoa (13). In addition, there is interest in studying the effect of SOD on the aging process (14).
The exploration of the therapeutic potential of human SOD has been limited mainly due to its limited availability.
Superoxide dismutase is also of interest because of its anti-inflammatory properties (11). Bovine-derived superoxide dismutase (orgotein) has been recognized to possess anti-inflammatory properties and is currently marketed in parts of Europe as a human pharmaceutical.
It is also sold in the United States as a veterinary product, particularly for the treatment of inflamed tendons in horses. However, supplies of orgotein are limited. Prior techniques involving recovery from bovine or other animal cells have serious limitations and the orgotein so obtained may produce allergic reactions in humans because of its non-human origin.
Copper zinc superoxide dismutase (CuZn SOD) is the most studied and best characterized of the various forms of superoxide dismutase.
Human CuZn SOD is a dimeric metallic-protein composed of identical non-covalently linked subunits, each having a molecular weight of 16,000 daltons and containing one atom of copper and one of zinc (5). Each subunit is composed of 153 amino acids whose sequence has been established (6,7).
The cDNA encoding human CuZn superoxide dismutase has been cloned (8). The complete sequence of the cloned DNA has also been determined (9). Moreover, expression vectors containing DNA encoding superoxide dismutase for the production and recovery of superoxide dismutase in bacteria have been described (24,25). The expression of a superoxide dismutase DNA and the production of SOD in yeast has also been disclosed (26).
Recently, the CuZ n SOD gene locus on human chromosome 21 has been characterized (27) and recent developments relating to CuZn superoxide dismutase have been summarized (28).
Much less is known about manganese superoxide dismutase (MnSOD). The MnSOD of E. coli K-12 has recently been cloned and mapped (22). Barra et al. disclose a 196 amino acid sequence for the MnSOD polypeptide isolated from human liver cells (19). Prior art disclosures differ, however, concerning the structure of the MnSOD molecule, particularly whether it has two or four identical polypeptide subunits (19,23). It is clear, however, that the MnSOD polypeptide and the CuZn SOD polypeptide are not homologous (19). The amino acid sequence homologies of MnSODs and FeSOD from various sources have also been compared (18).
Baret et al. disclose in a rat model that the half life of human MnSOD is substantially longer than the half-life of human copper SOD; they also disclose that in the rat model, human MnSOD and rat copper SOD are not effective as anti-inflammatory agents whereas bovine copper SOD and human copper SOD are fully active (20).
McCord et al. disclose that naturally occurring human manganese superoxide dismutase protects human phagocytosing polymorphonuclear (PMN) leukocytes from superoxide free radicals better than bovine or porcine CuZn superoxide dismutase in "in vitro" tests (21).
The present invention concerns the preparation of a cDNA molecule encoding the human manganese superoxide dismutase polypeptide or an analog or mutant thereof. It is also directed to inserting this cDNA into efficient bacterial expression vectors, to producing human MnSOD polypeptide, analog, mutant and enzyme in bacteria, to recovering the bacterially produced human MnSOD polypeptide, analog, mutant or enzyme. This invention is also directed to the human MnSOD polypeptides, analogs, or mutants thereof so recovered and their uses.
This invention further provides a method for producing enzymatically active human MnSOD in bacteria, as well as a method for recovering and purifying such enzymatically active human MnSOD.
The present invention also relates to a DNA molecule encoding the human MnSOD gene. It is also directed to inserting the DNA into mammalian cells to produce MnSOD polypeptide, analog, mutant and enzyme.
The present invention also relates to using human manganese superoxide dismutase or analogs or mutants thereof to catalyze the reduction of superoxide radicals to hydrogen peroxide and molecular oxygen. In particular, the present invention concerns using bacterially produced MnSOD or analogs or mutants thereof to reduce reperfusion injury following ischemia and prolong the survival period of excised isolated organs. It also concerns the use of bacterially produced MnSOD or analogs thereof to treat inflammations.